1. Field of the Invention
The present invention relates to an image pickup lens, an image pickup apparatus, and a lens controlling method.
2. Description of the Related Art
So-called power zoom/power focus mechanisms use a lens driving motor to electrically control lens actions and have recently been frequently used as means for moving the lens in accordance with photographer's manipulations. In this case, an electronic ring that serves as a manipulator and a volume key or the like configured to measure a manipulation amount are provided, and an electronic signal is output in accordance with the manipulation amount. Zooming and focusing can be realized by controlling the lens driving motor in accordance with the electric signal.
Japanese Laid-Open Patent Application No. (“JP”) 2004-233892 discloses an image pickup apparatus configured to drive a magnification variable lens using a magnification variable ring and a zoom key, and to use a potentiometer as a position detector of the magnification variable ring. JP 2004-233892 provides a motor configured to drive the magnification variable ring and a sensor configured to detect whether the magnification variable ring is located at the reference position, detects the output voltage of the potentiometer when the magnification variable ring is located at the reference position, and corrects fluctuations caused by temperature drift.
For example, assume that the photographer fixes the image pickup apparatus on a tripod, sets the magnification and focusing of the lens utilizing a zoom ring and a focus ring, and then turns off the power of the image pickup apparatus. Later on, when the power of the image pickup apparatus is turned on, it is convenient that the lens is located at the same position as the previous position.
However, when the focal length indication of the zoom ring does not correspond to the position of the variator lens unit, JP 2004-233892 drives the zoom motor in a direction of eliminating the difference. Therefore, when the output of the position of the zoom ring fluctuates due to the above temperature changes, the lens position shifts. This positional shift occurs when the manipulation of the manipulator switches from an invalid state to a valid state, etc. in addition to power switching from the turning-off state to the turning-on state.
In addition, the detecting accuracy of the potentiometer degrades due to the influence of electric noises. As a result, the positioning accuracy of the lens calculated from the detection result of the potentiometer degrades, and the lens position cannot be accurately calculated or shifts.